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## SAT

### Course: SAT > Unit 6

Lesson 6: Additional Topics in Math: lessons by skill- Volume word problems | Lesson
- Right triangle word problems | Lesson
- Congruence and similarity | Lesson
- Right triangle trigonometry | Lesson
- Angles, arc lengths, and trig functions | Lesson
- Circle theorems | Lesson
- Circle equations | Lesson
- Complex numbers | Lesson

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# Angles, arc lengths, and trig functions | Lesson

## What are "angles, arc lengths, and trig functions" problems, and how frequently do they appear on the test?

**Note:**On your official SAT, you'll likely see at most

**1 question**that tests your knowledge of the skills we teach in this article. Make sure you understand the more frequently-tested skills on the SAT before you spend time practicing this skill.

The problems in this lesson involve circles and angle measures in

**radians**, a unit for angle measure much like degrees. We can use radian measures to calculate arc lengths and sector areas, and we can calculate the sine, cosine, and tangent of radian measures.In this lesson, we'll learn to:

- Convert between radians and degrees
- Use our knowledge of special right triangles to find radian measures
- Identify the sine, cosine, and tangent of common radian measures

This lesson builds upon the following skills:

**You can learn anything. Let's do this!**

## How do I convert between radians and degrees?

### Radians & degrees

### Converting between radians and degrees

At the beginning of each SAT math section, the following information about radians and degrees is provided as reference:

- The number of degrees of arc in a circle is 360.
- The number of radians of arc in a circle is 2, pi.

This means 360 degrees is equivalent to 2, pi radians, and 180 degrees is equivalent to pi radians. We can set up a proportional relationship to convert between radian and degree measures.

**Example:**Convert 90, degrees to radians.

This also means we can use radian measures to calculate arc lengths and sector areas just like we can with degree measures:

**Example:**In a circle with center O, central angle A, O, B has a measure of start fraction, 2, pi, divided by, 3, end fraction radians. The area of the sector formed by central angle A, O, B is what fraction of the area of the circle?

### Try it!

## How do I use special right triangles to find radian measures?

**Note:**The topics covered in this section have not appeared in recent SATs, but they could in the future! If they do, it will likely only be

**1 question**.

### Trig values of special angles

### Special right triangles in circles

At the beginning of each SAT math section, the following information about special right triangles is provided as reference:

These angle measures and their radian equivalents appear frequently in questions about circles and circle trigonometry. The table below shows the angles in special right triangles and their equivalent radian measures.

Degree measure | Radian measure |
---|---|

30, degrees | start fraction, pi, divided by, 6, end fraction |

45, degrees | start fraction, pi, divided by, 4, end fraction |

60, degrees | start fraction, pi, divided by, 3, end fraction |

The radian measures we'll see on the SAT are usually multiples of the ones shown above.

On the test, we may be asked to find the radian measure of a central angle in a circle in the x, y-plane, such as that of angle A, O, B in the figure below. To do so, we'll draw a right triangle and look for the side length relationships in the special right triangles above.

We can draw a right triangle using the radius start overline, O, A, end overline as the hypotenuse. Since one vertex of the right triangle is the origin, the two legs of the right triangle have lengths equal to the x- and y- coordinates of point A.

Since the two legs of the right triangle have the same length, we can conclude that it is a 45-45-90 special right triangle, and the measure of angle A, O, B must be 45, degrees or start fraction, pi, divided by, 4, end fraction radians.

### Try it!

## How do I find the sine, cosine, and tangent of radian measures?

**Note:**The topics covered in this section have not appeared on recent tests, but they could show up on future tests! Questions on trigonometry in radians are a rare variety of an already infrequently-tested skill.

### Unit circle definition of trig functions

### The trig functions & right triangle trig ratios

### Trigonometry using radian measures

Trigonometry using radian measures is based on the

**unit circle**, a circle centered on the origin with a radius of 1.We can describe each point left parenthesis, x, comma, y, right parenthesis on the circle and the slope of any radius in terms of theta:

- x, equals, r, cosine, theta, equals, cosine, theta
- y, equals, r, sine, theta, equals, sine, theta
- start fraction, y, divided by, x, end fraction, equals, tangent, theta

The table below shows the sine, cosine, and tangent of some common radian measures in the unit circle:

**Note:**If you already know these, that's great! If not, consider spending time on the more frequently-tested skills on the SAT before familiarizing yourself with the values of trigonometric functions.

theta | x or cosine, theta | y or sine, theta | tangent, theta |
---|---|---|---|

0 | 1 | 0 | 0 |

start fraction, pi, divided by, 6, end fraction | start fraction, square root of, 3, end square root, divided by, 2, end fraction | start fraction, 1, divided by, 2, end fraction | start fraction, square root of, 3, end square root, divided by, 3, end fraction |

start fraction, pi, divided by, 4, end fraction | start fraction, square root of, 2, end square root, divided by, 2, end fraction | start fraction, square root of, 2, end square root, divided by, 2, end fraction | 1 |

start fraction, pi, divided by, 3, end fraction | start fraction, 1, divided by, 2, end fraction | start fraction, square root of, 3, end square root, divided by, 2, end fraction | square root of, 3, end square root |

start fraction, pi, divided by, 2, end fraction | 0 | 1 | undefined |

start fraction, 2, pi, divided by, 3, end fraction | minus, start fraction, 1, divided by, 2, end fraction | start fraction, square root of, 3, end square root, divided by, 2, end fraction | minus, square root of, 3, end square root |

start fraction, 3, pi, divided by, 4, end fraction | minus, start fraction, square root of, 2, end square root, divided by, 2, end fraction | start fraction, square root of, 2, end square root, divided by, 2, end fraction | minus, 1 |

pi | minus, 1 | 0 | 0 |

## Your turn!

## Things to remember

We can describe each point left parenthesis, x, comma, y, right parenthesis on the unit circle and the slope of any radius in terms of theta:

- x, equals, cosine, theta
- y, equals, sine, theta
- start fraction, y, divided by, x, end fraction, equals, tangent, theta

## Want to join the conversation?

- what does the symbol θ represent(2 votes)
- It is just a substitute for an angle you don’t know. Kind of like variables.(8 votes)

- I'm a little bit confused...Where in the SAT math courses on Khan Academy do I find more about it?(1 vote)
- If you want more practice on this, you can go to the practice tab in your SAT dashboard and scroll down in the math section until you get to "Angles, arc lengths, and trig functions" under Additional Topics in math. If you want some more learning, check out some videos in Khan's high school geometry course, outside of the SAT section. Did that answer your question?(9 votes)

- Is there a pattern or a way to intuitively understand the values of trigonometric functions or is memorization the only approach to remember the sine, cosine, and tangent of some common radian measures in the unit circle?(2 votes)
- Well you can check the derivations for how we got these values, maybe that might help? The values are now embedded in my mind from practice and memorization.

BUT since you were asking for a trick/pattern to remember the table, here's something my tenth grade math teacher taught us (though I've never had the need to use it):

^ First remember the order of the angles:**0, pi/6, pi/4, pi/3 and pi/2**

^ For the sin table, write the numbers**0, 1, 2, 3, 4**under each angle*respectively*

^ Now take the square root of the numbers and THEN divide them by 2

You'll be left with:**Angle Sintheta**

0 0

pi/6 1/2

pi/4 rt.2/2

pi/3 rt.3/2

pi/2 1

^ Now for cosx it's just the other way around: 1, rt.3/2 etc

^ For tan it's just sin/cos

Hope this helps!!(3 votes)

- For people who have recently take the SAT, are Trig funcions on it. It says in the guide here that it use to apear on the Sat but not anymore but might in the furture.(1 vote)
- There is a small chance you would have to do trig questions on the SAT. Maybe less than 5 questions per test would focus on this. I'm not sure if this applies to the 2023 redesign of the SAT or not, because that math section is of course subject to change from the one we have right now.

As for trig, you'll have to know the basic meaning of the trig ratios sine, cosine, and tangent on a right triangle, how to convert degrees to radians, a very basic understanding of the unit circle, and the fact that sin(x) = cos(90 - x).(3 votes)

- At the very last question how did we determine that we are using the 60 degree angle or angle aob to find a and what do we ean when we say a(1 vote)
- So, I'm alright if I'm using a calculator on these problems. However, it's mainly in the No Calculator section. How would I go about doing this (especially in the use of pi), besides just being fantastic at mental math? Thanks.(1 vote)
- I would just advise you to practice doing SAT non calc problems. The more practice you do, the better you will get at doing the mental math faster and more efficiently. Hope this helps!(1 vote)